In the modern aircraft industry, it is sometimes necessary to rework existing fastener holes in metallic aircraft skins and panels in-situ. The fasteners used today are often precision-fit or interference-fit fasteners, which require precise tolerances on the holes they are to be used in conjunction with. The holes may be reworked for the purpose of removing any surface scratches or marks around a hole that may affect the structural integrity of the joint under high load conditions. Even miniscule surface defects may act as stress raisers and invoke rapid crack propagation through a structure if left unattended under severe load conditions.
Removing a structural component for rework can be difficult and time consuming and may introduce more potential problems. It is therefore necessary to be able to rework holes in all locations of the aircraft skin, including tight confined areas, under the wings, under the fuselage and around obstructions. The rework may consist of drilling holes or reaming holes to return them to precise tolerances. This may require rework of miniscule increments, often carried out with a hand held electric or air operated drill or reamer. Due to the difficulty of accessing these locations it is common for this kind of rework to be done by hand but this causes other potential problems.
Due to the precise nature of the holes to be drilled, a recurring problem is with the alignment of a hand held drill or reamer. The tolerances to be met when reworking a hole may be as small an increase as 0.004 of an inch in diameter. As the ratio of diameter to length on some fastener holes can be large, the alignment of the drill or reamer is important. Any misalignment of the hand held rework tools will lead to the hole no longer remaining round along its full bore.
It is important not just to remove surface defects and scratches but to maintain a constant round hole for the application of the new fastener. All reworked holes are examined, and must pass examination, before an aircraft can be certified safe to go back into service. Further rework will be required if reworked holes do not meet requirements, to maintain the aircraft's structural life. If holes cannot be reworked to the necessary tolerances, the aircraft wing or fuselage may become functionally ineffective and may be junked.
It would be desirable to address or ameliorate one or more shortcomings or disadvantages associated with prior methods and devices for drilling or reworking of fastener holes in structures, or to at least provide a useful alternative thereto.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.